2. Please switch on debug mode by adding the following line to your config.php file:

$debug='1';

Are there any additional errors reported on top of the page?

3. You can test if this is problem also exists at the latest version by testing our online demo at demo.limesurvey.org/admin(external link) which always runs the latest Limesurvey version.
Username: admin
Password: test
If you can reproduce the problem there please report back.

It was being blocked by spam filters due to the optout keyword and using a raw IP address. We are going to use a resolved server and try again. We are also going to try to use an image instead of the word optout and change the name of the optout.php page to prevent other spam triggers from blocking. Nothing wrong with Limesurvey.
Thank you for your help.